Bromine-based sulfamate stabilized breaker composition and process

ABSTRACT

A process for reducing the viscosity of fracturing fluids in downhole oilfield operations is provided. The process comprises contacting a sulfamate stabilized, bromine-based breaker with an aqueous polysaccharide fracturing fluid, with the breaker present in an amount to reduce the viscosity of the fracturing fluid. A composition which comprises a sulfamate stabilized, bromine-based breaker for use in decreasing the viscosity of an aqueous polysaccharide fracturing fluid for use in subterranean oil and gas wells is also provided.

REFERENCE TO RELATED APPLICATION

This application is a continuation of commonly-owned application Ser.No. 10/802,349, filed Mar. 16, 2004, now U.S. Pat. No. 7,223,719, issuedMay 29, 2007, the disclosure of which is incorporated herein byreference.

TECHNICAL FIELD

This invention relates to a breaker for effecting viscosity decreases inaqueous fracturing fluids generally used in the workover of subterraneanoil and gas wells. The invention relates to a new breaker compositionthat provides effective viscosity decreases in such oil and gas wellactivities.

BACKGROUND

Breakers (often referred to as breaker fluids) are often used in the oilor gas field for decreasing the viscosity of oilfield fracturing fluidsafter the fracturing is completed. While breakers that reduce viscosityin downhole operations are available, further improvements inperformance are desired. For example, a breaker fluid that could providea controlled rate of viscosity decay would be of considerable advantage.

Breakers can be mixed with the fracturing fluid, or added later asneeded. It is preferable to mix the breaker (fluid) with the fracturingfluid; however, it is disadvantageous to mix some of the known breakerswith the fracturing fluid. Also, some breakers, particularly bleach,corrode metal pipe, which is normally used in drilling, workover, andcompletion operations. It would be especially advantageous if thebreaker fluid in addition to providing a controlled rate of viscositydecay, would cause minimal corrosion of metal pipes, and could be mixedwith the fracturing fluid.

SUMMARY OF THE INVENTION

This invention enables the achievement of most, if not all, of the abovedesirable advantages in a highly cost-effective manner. The breakercomposition provided by this invention causes minimal corrosion of metalpipe. Breaker compositions of this invention work over a wider pH rangethan do those that are chlorine-based. Further, some of the breakercompositions provided by the invention can give a controlled rate ofviscosity decay, and thus can be mixed with the oilfield fracturingfluid without significant premature viscosity decreases of thefracturing fluid, which in turn avoids a second treatment to break thefracturing fluid polymer, thereby saving rig time and handlingequipment. Surprisingly, the rate of viscosity decay can be controlledby pH adjustments when using a breaker composition of this invention.

Provided by this invention is a process which comprises contacting asulfamate stabilized, bromine-based breaker with an aqueouspolysaccharide fracturing fluid. The fracturing fluid is for use insubterranean oil and gas wells, primarily during workover, and thebreaker is present in an amount to reduce the viscosity of thefracturing fluid. Preferably, the breaker is formed from (A) a halogensource which is (i) bromine chloride, (ii) bromine and chlorine, (iii)bromine, or (iv) a mixture of any two or more of (i), (ii), and (iii),(B) a source of sulfamate anions, (C) alkali metal base, and (D) water,in amounts that the breaker has an active bromine content of at least50,000 ppm, and an atom ratio of nitrogen to active bromine originatingfrom (A) and (B) that is greater than about 0.93.

Also provided by this invention is a composition for use in decreasingthe viscosity of aqueous polysaccharide fracturing fluids, which aregenerally used in the workover of subterranean oil and gas wells. Thecomposition is comprised of a sulfamate stabilized, bromine-basedbreaker. In preferred embodiments of this invention, the breakercomposition is formed from (A) a halogen source which is (i) brominechloride, (ii) bromine and chlorine, (iii) bromine, or (iv) a mixture ofany two or more of (i), (ii), and (iii), (B) a source of sulfamateanions, (C) alkali metal base, and (D) water, in amounts that thebreaker has an active bromine content of at least 50,000 ppm, and anatom ratio of nitrogen to active bromine originating from (A) and (B)that is greater than about 0.93.

Preferred breakers are those in which the halogen source is brominechloride, bromine and chlorine, or a mixture of bromine chloride andbromine, and the alkali metal base is a sodium or potassium base. Morepreferred breakers are those wherein the halogen source consistsessentially of bromine chloride, wherein the alkali metal base is asodium base, wherein the active bromine content of the breaker is atleast 100,000 ppm, the above atom ratio of nitrogen to active bromineoriginating from (A) and (B) is at least about 1, and/or the pH of thebreaker is at least about 12. Still more preferred are breakers whichhave two or more of these preferred characteristics; highly preferred isa breaker that has all of the foregoing preferred characteristics.Particularly preferred breakers are those wherein the halogen sourceconsists essentially of bromine chloride, wherein the alkali metal baseis sodium hydroxide, wherein the active bromine content of the breakeris at least 140,000 ppm, the above atom ratio of nitrogen to activebromine originating from (A) and (B) is at least about 1.1, and/or thepH of the breaker is at least about 13. More particularly preferred arebreakers that have at least two of these particularly preferredcharacteristics; the most highly preferred breaker has all of theseparticularly preferred characteristics.

Also more preferred breakers for use in this invention are highlyconcentrated aqueous sulfamate-stabilized active bromine compositionswhich are solids-free aqueous solutions or solids-containing slurriesformed as above, and in which the content of dissolved active bromine isgreater than about 160,000 ppm. In the preferred aqueous solutions ofthis type, the active bromine in these preferred breakers is all insolution at room temperature (e.g., 23° C.). In one particularlypreferred embodiment the content of active bromine in such aqueousbreaker solutions (whether formed from use of (a) BrCl, or (b) Br₂, or(c) BrCl and Br₂, or (d) Br₂ and Cl₂, or (e) BrCl, Br₂ and Cl₂) is inthe range of about 176,000 ppm to about 190,000 ppm (wt/wt). In anotherparticularly preferred embodiment the content of active bromine in suchaqueous breaker solutions (whether formed from use of (a) BrCl, or (b)Br₂, or (c) BrCl and Br₂, or (d) Br₂ and Cl₂, or (e) BrCl, Br₂ and Cl₂)is in the range of from about 201,000 ppm to about 215,000 ppm.

Also suitable for use in this invention is a solid statebromine-containing breaker formed by removal of water from an aqueoussolution or slurry of a product formed in water from (I) a halogensource which is (i) bromine, (ii) bromine chloride, (iii) a mixture ofbromine chloride and bromine, (iv) bromine and chlorine in a Br₂ to Cl₂molar ratio of at least about 1, or (v) bromine chloride, bromine, andchlorine in proportions such that the total Br₂ to Cl₂ molar ratio is atleast about 1; and (II) a source of overbased sulfamate which is (i) analkali metal salt of sulfamic acid and/or sulfamic acid, and (ii) analkali metal base, wherein said aqueous solution or slurry has a pH ofat least 7, preferably above 10 and more preferably above 12, and anatom ratio of nitrogen to active bromine from (I) and (II) of greaterthan 0.93. The concentration of the product formed in water from (I) and(II) used in forming the solid state bromine-containing breaker is notcritical; any concentration can be present in the initial aqueoussolution or slurry. Naturally it is desirable to start with a moreconcentrated solution or slurry as this lessens the amount of water thatmust be removed when preparing the solid state bromine-containingbreaker.

The solid state bromine-containing breakers of this invention arepreferably formed by spray drying the aqueous solution or slurry of theproduct formed from (I) and (II) above. Temperatures of the atmosphere(e.g., dry air or nitrogen) into which the spray is directed istypically in the range of about 20 to about 100° C., and preferably isin the range of about 20 to about 60° C., particularly when the processis carried out at reduced pressure. When spray drying is used it ispreferred to use the product formed from (I) and (II) as a solutionrather than as a slurry as this minimizes the possibility of nozzlepluggage. On the other hand, if the water is to be flashed off orotherwise distilled from the solution or slurry of the product formedfrom (I) and (II), it is preferred to use the product formed from (I)and (II) as a slurry rather than as a solution as this minimizes theamount of water to be removed. Such flashing or distillations can be,and preferably are, conducted at reduced pressures to reduce thetemperatures to which the product formed from (I) and (II) is exposedduring drying.

The solid state bromine-containing breakers of this invention aretypically in the form of powders or relatively small particles. Howeverthe solid state bromine-containing breakers of this invention can becompacted into larger forms such as nuggets, granules, pellets, tablets,pucks, and the like, by use of known procedures. Such compacted productsmay be formed with the use of binding agents or other materials thatcause the particles to adhere one to another. If the binder used is notreadily soluble in water, it is important not to totally encapsulate theproduct with a water-impervious coating of such binder that remainsintact under actual use conditions, as this would prevent contactbetween the encapsulated bromine-containing breaker and the water beingtreated with the breaker. Low melting waxes or the like may be used tobind and even to encapsulate the bromine-containing breaker in caseswhere the encapsulated product is used in waters at high enoughtemperatures to melt off the coating and bindings so that the water cancome into contact with the previously encased breaker itself. However,use of binding substances that are water-soluble or that provideeffective binding action in proportions insufficient to encapsulate theparticles being bound together, is preferable. The binding agent usedshould be compatible with the solid state bromine-containing breaker ofthis invention.

These and other embodiments and features of this invention will be stillfurther apparent from the ensuing description and appended claims.

FURTHER DETAILED DESCRIPTION OF THE INVENTION

The breakers used in the practice of this invention are known. Methodsfor their preparation are given, for example, in U.S. Pat. Nos.3,558,503; 6,068,861; 6,110,387; 6,299,909 B1; 6,306,441 B1; and6,322,822 B1.

Generally, there are two methods for combining the fracturing fluid andthe breaker. In one method, the breaker is mixed with the fracturingfluid prior to sending the fracturing fluid downhole. This method isfavored at least because of convenience—it is easier to mix the fluidsat the surface and send one mixture downhole. A disadvantage of thisblending method is that the breaker can decrease the viscosity of thefracturing fluid before the desired time. In another method, thefracturing fluid is is sent downhole, and the breaker is sent downholelater. While sending the breaker downhole later is inconvenient, in thismethod the breaker does not decrease the viscosity of the fracturingfluid prematurely.

The breakers of the present invention are suitable for use in eithermethod for combining the fracturing fluid and the breaker. For example,the viscosity of xanthan and simple guar fracturing fluids with pH 7appear to be immediately broken by a breaker of the invention, which isuseful when the breaker is sent downhole later (after the fracturingfluid). Breakers of the invention are also useful when the fracturingfluid and the breaker are combined before the fracturing fluid is sentdownhole. As an example, a breaker of the invention breaks the viscosityof a pH 10.5 guar-viscosified fracturing fluid after a desirable timelag.

Blending of the breaker with the fracturing fluid can be conducted inany manner conventionally used in blending well fluids generally. Sincethe breakers, including the preferred breakers, whether formed on siteor received from a manufacturer, are normally mobile aqueous solutions,the blending is rapid and facile. Simple metering or measuring devicesand means for mixing or stirring the breaker with the fracturing fluidcan thus be used, if desired. Periodically individual batches offracturing fluids can be treated with the breaker and used so that thebreaker is provided intermittently to the well. Preferably, however, allof the fracturing fluid used in a given operation is treated with abreaker of this invention so that the breaker is continuously beingprovided to the well.

Typically the amount of the breaker used should provide in the range ofabout 1 to about 10,000 ppm, and preferably in the range of about 100 toabout 2000 ppm of active bromine species in the blended well fluid priorto well application. Departures from these ranges whenever deemednecessary or desirable are permissible and are within the scope of thisinvention.

The breaker is used in an amount sufficient to reduce the viscosity ofthe fracturing fluid, and preferably the viscosity is reduced to aboutthe viscosity value of the fracturing fluid prior to the addition of thepolysaccharide thickening agent. The amount of breaker needed oftenvaries depending upon the temperature of the fracturing fluid, theconcentration of the viscosifying polymer in the fracturing fluid, andthe pH of the fracturing fluid.

While breakers made by use of bromine can be used (e.g., U.S. Pat.No.3,558,503) as the sulfamate stabilized, bromine-based breakers ofthis invention, preferred breakers of this invention because of theireffectiveness and stability are formed from bromine chloride, bromineand chlorine, or a mixture of bromine chloride and up to about 50 mole %of bromine. A particularly preferred breaker of this type for use in thepractice of this invention is commercially available from AlbemarleCorporation under the trademark WELLGUARD™ 7137. The sulfamate used inthe production of such breaker products is effective in stabilizing theactive bromine species over long periods of time, especially when the pHof the product is at least about 12 and preferably at least about 13.For example, WELLGUARD™ 7137 breaker is stable for greater than one yearif protected from sunlight. For ease of reference, these preferredhighly effective and highly stable breakers for use in the practice ofthis invention formed from bromine chloride, bromine and chlorine, or amixture of bromine chloride and up to about 50 mole % of bromine, asulfamate source such as sulfamic acid or sodium sulfamate, a sodiumbase, typically NaOH, and, normally, water are often referred tohereinafter collectively as “preferred breakers” or “the preferredbreakers”, and in the singular as “preferred breaker” or “the preferredbreaker”. The breaker of this invention is usually in liquid form, but,as described above, the breaker can be in the solid state. When inliquid form, the breaker of this invention may be referred to as a“breaker fluid”.

Some components or impurities commonly encountered in or by aqueous wellfluids are reactive with the breakers used pursuant to this invention.One such impurity is hydrogen sulfide. Another such impurity is oil,particularly hydrocarbonaceous oil. Such components are identifiable assubstances which are reactive in aqueous media with monobromo alkalimetal sulfamate, dibromo alkali metal sulfamate, orbromonium ions. Whensuch components are present, their presence can be overcome provided thequantity of such components can be effectively overcome by use of asacrificial quantity of a breaker used pursuant to this invention.Polyacrylamide and scale inhibitor are examples of potential additivesor components of the aqueous well fluid. Such common well fluidcomponents are surprisingly compatible with breakers employed in thepractice and compositions of this invention. Starch, on the other hand,is an example of a potential well fluid component which is notnecessarily compatible with breakers of this invention. The presence ofstarch and like components in the well fluid similarly may be overcomeusing a sacrificial quantity of the breaker. Thus, another embodiment ofthis invention is a process for effecting breaker activity in an aqueouswell fluid that contains one or more components reactive with monobromoalkali metal sulfamate, dibromo alkali metal sulfamate or bromoniumions, which process comprises blending an aqueous breaker of thisinvention with the aqueous well fluid.

One of the advantages of using the preferred breakers is their greatcompatibility with other components used in downhole operations. Forexample, unlike HOBr and hypobromites, the preferred breakers do notoxidize or otherwise destroy organic phosphonates typically used ascorrosion and scale inhibitors. In fact, the preferred breakers arecompatible with polyacrylamide-containing slickwater fracturing fluidsas long as they are devoid or substantially devoid of hydrogen sulfide.Hydrogen sulfide can react rapidly with the breakers used pursuant tothis invention, including the preferred breakers. Therefore, if there issome hydrogen sulfide present in the aqueous fracturing fluid, it ispreferred to determine analytically the amount of hydrogen sulfide thatis present in the downhole solution. If the amount is sufficiently smallthat it does not require an excessive amount of the breaker to consumethat amount of hydrogen sulfide, the amount of the breaker injected intothe well should be sufficient not only to consume the hydrogen sulfidebut additionally to provide a suitable residual quantity of activebromine in the well. Since at least the preferred breakers are highlycost-effective, it is economically feasible to sacrifice some of thebreaker as a means of destroying the hydrogen sulfide so that theremainder of the breaker used can provide the appropriate amount ofviscosity decrease to the fracturing fluid. Of course if the amount ofhydrogen sulfide is so high as to make it non-feasible economically todestroy the hydrogen sulfide using the breaker, the use of thecompositions of this invention in such well is not recommended. Thedividing line as between how much hydrogen sulfide can be tolerated andconsumed with extra breaker pursuant to this invention and how muchmakes it non-feasible to do so will vary depending upon a number ofvariable economic factors as well as technical factors. For example,such factors as operating costs, well location, particular breaker beingused, and the amount of viscosity decrease needed or desired downholecan have a significant effect upon how much hydrogen sulfide can betolerated in any given situation. Therefore, the amount of hydrogensulfide that can be tolerated and overcome in the downhole aqueous fluidpursuant to this invention is subject to considerable latitude andcannot be universally quantified. Suffice it to say that the well beingtreated and/or the water used in forming the fracturing fluid shouldeither be free of hydrogen sulfide or may contain in the downholeaqueous fluid a “consumable amount” of hydrogen sulfide. The “consumableamount” of hydrogen sulfide that can be tolerated can be, and should be,determined on a small scale experimentally before conducting a fullscale operation.

As is known in the art, aqueous well fluids can contain various additivecomponents including proppants such as calcium carbonate, and pecanshells; viscosity modifying agents such as ferrochrome lignosulfonate,calcium lignosulfonate, or sodium lignosulfonate; emulsifiers;surfactants; pH control agents; clay stabilizers; and the like, as longas such optional ingredients do not adversely affect the fracturingfluid and/or breaker. The aqueous well fluids can also optionallycontain crosslinkers, including borates, chromates, titanates,zirconates, aluminates, and antimony crosslinking agents, and the like.

The fracturing fluids to which the breakers of this invention impartviscosity decreases are aqueous polysaccharide fracturing fluids, alsoknown as gel-type fracturing fluids. Various gelation agents andcrosslinking agents can be used as the polysaccharide thickening agentof the fracturing fluid. The fracturing fluid thickening agent caneither be a synthetic polymer or a natural gum. Synthetic polymersinclude acrylic polymers, vinyl polymers, and cellulose derivatives. Thesynthetic polymers most frequently used are polyacrylamide andhydroxyethylcellulose. Polysaccharides which may be present in thefracturing fluids are the industrial gums such as those generallyclassified as exudate gums, seaweed gums, seed gums, microbialpolysaccharides; and hemicelluloses (cell wall polysaccharides found inland plants) other than cellulose and pectins. These polysaccharidesinclude xylan, mannan, galactan, L-arabino-xylans,L-arabino-D-glucurono-D-xylans; 40-methyl-D-glucurono-D-xylans,D-gluco-D-mannans; D-galacto-D-mannans and arabino-D-galactans, algin,such as sodium alginate, carrageenin, fucordan, laminaran, agar, gumarabic, gum ghatti, gum karaya, tamarind gum, tara, konjak, carrageenan,tragacanth gum, guar gum and derivatives thereof, xanthan gums, locustbean gums and the like. Modified gums such as carboxyalkyl derivatives(e.g., carboxymethyl guar and hydroxyalkyl derivatives, e.g.,hydroxyethyl guar and hydroxypropyl guar) can also be employed. Modifiedcelluloses and derivatives thereof can also be employed, for example,hydroxyethylcellulose, carboxymethylcellulose, andcarboxymethylhydroxyethylcellulose, and the like. Natural gums,especially xanthan gum and guar gum, are preferred over the syntheticpolymers.

The breakers of the invention can provide a controlled rate of viscositydecay, allowing the breaker to be mixed with the fracturing fluid,avoiding a second treatment (downhole) to break the fracturing fluidpolymer. As stated before, the rate of viscosity decay can be controlledby pH adjustments when using a breaker of this invention. Thus usage ofthe breakers of this invention can shorten and simplify the wellheadoperations in this regard.

Still another advantage of this invention is the very low corrosivity ofthe preferred breakers against metals, especially ferrous metals. Thisis the result of the low oxidation-reduction potential of the preferredbreakers.

Yet another advantage of this invention is the stability of at least thepreferred breakers at elevated temperatures. Thus unlike HOBr orhypobromite solutions which have relatively poor thermal stability atelevated temperatures, the preferred breakers can be used in very deepwells where highly elevated temperatures are encountered withoutpremature decomposition.

Standard analytical test procedures are available enabling closeapproximation of “total bromine” and “free bromine” present in anaqueous breaker solution. For historical and customer familiarityreasons, these procedures actually express the results of thedeterminations as “free chlorine” and “total chlorine”, which resultscan then be arithmetically converted to “total bromine” and “freebromine”. The procedures are based on classical test procedures devisedby Palin in 1974. See A. T. Palin, “Analytical Control of WaterDisinfection With Special Reference to Differential DPD Methods ForChlorine, Chlorine Dioxide, Bromine, Iodine and Ozone”, J. Inst. WaterEng., 1974, 28, 139. While there are various modernized versions of thePalin procedures, the version of the tests for “free chlorine” and“total chlorine” recommended herein for use, are fully described in HachWater Analysis Handbook, 3rd edition, copyright 1997. The procedure for“free chlorine” is identified in that publication as Method 8021appearing on page 335, whereas the procedure for “total chlorine” isMethod 8167 appearing at page 379. Briefly, the “free chlorine” testinvolves introducing to the halogenated water a powder comprising DPDindicator powder and a buffer. “Free chlorine” present in the waterreacts with the DPD indicator to produce a red to pink coloration. Theintensity of the coloration depends upon the concentration of “freechlorine” species present in the sample. This intensity is measured by acolorimeter calibrated to transform the intensity reading into a “freechlorine” value in terms of mg/L Cl₂. Similarly, the “total chlorine”test also involves use of DPD indicator and buffer. In this case, KI ispresent with the DPD and buffer whereby the halogen species present,including nitrogen-combined halogen, reacts with KI to yield iodinespecies which turn the DPD indicator to red/pink. The intensity of thiscoloration depends upon the sum of the “free chlorine” species and allother halogen species present in the sample. Consequently, thiscoloration is transformed by the colorimeter into a “total chlorine”value expressed as mg/L Cl₂.

In greater detail, these procedures are as follows:

-   1. To determine the amount of species present in the aqueous well    fluid water which respond to the “free chlorine” and “total    chlorine” tests, the sample should be analyzed within a few minutes    of being taken, and preferably immediately upon being taken.-   2. Hach Method 8021 for testing the amount of species present in the    sample which respond to the “free chlorine” test involves use of the    Hach Model DR 2010 colorimeter or equivalent. The stored program    number for chlorine determinations is recalled by keying in “80” on    the keyboard, followed by setting the absorbance wavelength to 530    nm by rotating the dial on the side of the instrument. Two identical    sample cells are filled to the 10 mL mark with the aqueous sample    under investigation. One of the cells is arbitrarily chosen to be    the blank. Using the 10 mL cell riser, this is admitted to the    sample compartment of the Hach Model DR 2010, and the shield is    closed to prevent stray light effects. Then the ZERO key is    depressed. After a few seconds, the display registers 0.00 mg/L Cl₂.    To a second cell, the contents of a DPD Free Chlorine Powder Pillow    are added. This is shaken for 10-20 seconds to mix, as the    development of a pink-red color indicates the presence of species in    the sample which respond positively to the DPD test reagent. Within    one minute of adding the DPD “free chlorine” reagent to the 10 mL of    aqueous sample in the sample cell, the blank cell used to zero the    instrument is removed from the cell compartment of the Hach Model DR    2010 and replaced with the test sample to which the DPD “free    chlorine” test reagent was added. The light shield is then closed as    was done for the blank, and the READ key is depressed. The result,    in mg/L Cl₂ is shown on the display within a few seconds. This is    the “free chlorine” level of the water sample under investigation.-   3. Hach Method 8167 for testing the amount of species present in the    aqueous sample which respond to the “total chlorine” test involves    use of the Hach Model DR 2010 calorimeter or equivalent. The stored    program number for chlorine determinations is recalled by keying in    “80” on the keyboard, followed by setting the absorbance wavelength    to 530 nm by rotating the dial on the side of the instrument. Two    identical sample cells are filled to the 10 mL mark with the water    under investigation. One of the cells is arbitrarily chosen to be    the blank. To the second cell, the contents of a DPD Total Chlorine    Powder Pillow are added. This is shaken for 10-20 seconds to mix, as    the development of a pink-red color indicates the presence of    species in the water which respond positively to the DPD “total    chlorine” test reagent. On the keypad, the SHIFT TIMER keys are    depressed to commence a three-minute reaction time. After three    minutes the instrument beeps to signal the reaction is complete.    Using the 10 mL cell riser, the blank sample cell is admitted to the    sample compartment of the Hach Model DR 2010, and the shield is    closed to prevent stray light effects. Then the “ZERO” key is    depressed. After a few seconds, the display registers 0.00 mg/L Cl₂.    Then, the blank sample cell used to zero the instrument is removed    from the cell compartment of the Hach Model DR 2010 and replaced    with the test sample to which the DPD “total chlorine” test reagent    was added. The light shield is then closed as was done for the    blank, and the READ key is depressed. The result, in mg/L Cl₂ is    shown on the display within a few seconds. This is the “total    chlorine” level of the water sample under investigation.-   4. To convert the readings to bromine readings, the “free chlorine”    and the “total chlorine” values should be multiplied by 2.25 to    provide the “free bromine” and the “total bromine” values.

Another procedure for measuring the total active halogen and brominechloride (BrCl) content in a solution are as follows:

-   1. To determine the amount of species present in the aqueous well    fluid water which respond to the “free chlorine” and “total    chlorine” tests, the sample should be analyzed within a few minutes    of being taken, and preferably immediately upon being taken.-   2. Standardize a 0.1 N sodium thiosulfate solution.-   3. Accurately weigh a sample (about 0.2-0.5 g to the nearest 0.1 mg)    into a 250 mL iodine flask containing 50 mL of acetic acid and a    magnetic stir bar. Record the weight as A grams. Swirl to dissolve    the sample, add 50 mL of distilled water and 25 mL of 15% KI    solution. Stir for 15 minutes.-   4. Titrate the sample with the standard 0.1 N sodium thiosulfate.    This can be done either potentiometrically using a platinum titrode    to detect the first derivative endpoint, or visually to a faint    yellow color. When the first derivative endpoint is reached, add 1    mL of starch solution and continue the dropwise addition of 0.1 N    sodium thiosulfate, while stirring, until the next addition    discharges the blue color. Record the volume of sodium thiosulfate    solution used as B mL. The average of at least two replications is    reported. Agreement between the replications should be within ±5%    relative. If agreement is greater than ±5%, two more samples are    run, and the average of all measurements is reported.-   5. Determine a reagent blank value by repeating steps 3 & 4, except    for weighing a sample. Record the volume as C mL.-   6. The calculations are as follows:

$\begin{matrix}{{Total}{\mspace{11mu}\;}\%\mspace{11mu}{Active}\mspace{14mu}{Halogen}} \\( {{as}\mspace{14mu}{Bromine}} )\end{matrix} = \frac{( {{B\mspace{11mu}{mL}} - {C\mspace{11mu}{mL}}} )( {N\mspace{14mu}{sodium}\mspace{14mu}{thiosulfate}} )(7.9904)}{A\mspace{14mu}{grams}}$where A grams=sample weight, B mL=titration volume for sample for totalactive halogen; and C mL=titration blank for total active halogen.

To convert to percent bromine chloride:% BrCl=(Total % Active Halogen)×(115.35/159.81)

The fraction is the molecular weight of bromine chloride divided by themolecular weight of Br₂.

The following examples are presented for purposes of illustration, andare not intended to impose limitations on the scope of this invention.

In the Examples, a group of experiments was conducted on a laboratoryscale using WELLGUARD™ 7137 (Albemarle Corporation) as the breaker.WELLGUARD™ 7137 is a sulfamate-stabilized, bromine-based breaker. Moreparticularly, the activity of the WELLGUARD™ 7137 breaker being used was10.8% or 108,000 ppm as BrCl (15.0% or 150,000 ppm as Br₂).

EXAMPLES

A stock solution of aqueous KCl (7 wt %) was prepared by stirring 271 gof KCl with 3600 mL of deionized water. A stock solution of aqueous KCl(7 wt %) with WELLGUARD™ 7137 was prepared by stirring 271 g of KCl with3600 mL of deionized water and 12.3 grams of WELLGUARD™ 7137. Theresidual breaker was measured at 981 ppm as total Br₂. This value wasused as the baseline at time=zero hours in Table 2. A mixer(Hamilton-Beach) was used for all stirring and shearing. The viscosityand bromine level were measured at regular intervals for each sample.

Brookfield viscosities were measured using spindle S-18 at ambienttemperature (19-25° C.). Significant decreases in the viscosity wereinterpreted as breakdown of the polymer (here, xanthan or guar).Residuals of the breaker (WELLGUARD™ 7137) were measured at 3 minutesusing the total chlorine reagent (DPD) with a hand-heldspectrophotometer (Hach DR/2000); results are reported as total Br₂.

Example 1

Xanthan gum

Two samples were made: one containing the WELLGUARD™ 7137 treatment, anda comparative sample not containing the WELLGUARD™ 7137 treatment. Toprepare the comparative sample, some of the stock solution of 7% aqueousKCl (356 g) was acidified to pH 3.6 with dilute HCl (0.1 M). To thissolution, xanthan (2.52 g; Kelco Kelzan XCD, CP Kelco) was added withstirring. This mixture was stirred for 3 minutes, neutralized to pH 7.1with dilute aqueous NaHCO₃ (0.1 M), and then sheared for 1 minute more.The sample of the invention was prepared by acidifying some of the stocksolution of aqueous KCl with WELLGUARD™ 7137 (357 g) to pH 4.5 withdilute HCl (0.1 M). To this solution, xanthan (2.52 g; Kelco Kelzan XCD)was added with stirring. This mixture was stirred for 3 minutes,neutralized to pH 7.1 with dilute aqueous NaHCO₃ (0.1 M), and thensheared for 1 minute more.

Table 1 summarizes the viscosity time dependence for these well fluids.In the xanthan fluid, WELLGUARD™ 7137 knocked down the viscosityrelatively quickly. One possible explanation for the slight increase inviscosity between hour 4 and hour 22 is continued hydration of thexanthan polymer. Table 2 summarizes the time dependence of the presenceof residual WELLGUARD™ 7137, measured as total Br₂, using a DPD assay.In the xanthan fluid, the residual decay is immediate: it plateaus andceases to change significantly. Conditions for the xanthan system werenot optimized.

Example 2

Guar gum

Two samples were made: one containing the WELLGUARD™ 7137 treatment, anda comparative sample not containing the WELLGUARD™ 7137 treatment. Toprepare the comparative sample, some of the stock solution of 7% aqueousKCl (357 g) was sheared for 3 minutes with guar (1.86 g; ChemplexIndustries, Inc.). This mixture was heated to 120° F. (49° C.), and keptat this temperature for the duration of the study. The sample of theinvention was prepared by shearing some of the stock solution of aqueousKCl with WELLGUARD™ 7137 (355 g) with guar (1.86 g; Chemplex) for 3minutes. This mixture was heated to 120° F. (49° C.), and kept at thistemperature for the duration of the study.

Table 1 summarizes the viscosity time dependence for these well fluids.In this guar system, WELLGUARD™ 7137 appeared to have completely brokenthe polymer already at hour 22. Table 2 summarizes the time dependenceof the presence of residual WELLGUARD™ 7137, measured as total Br₂. Inthis guar well fluid, the residual decay appears to occur quickly.

Example 3

Guar Gum; pH Adjusted to 10.5

Two samples were made: one containing the WELLGUARD™ 7137 treatment, anda comparative sample not containing the WELLGUARD™ 7137 treatment. Toprepare the comparative sample, some of the stock solution of 7% aqueousKCl (355 g) was basified to pH 10.5 with Na₂CO₃. This solution wassheared for 3 minutes with guar (3.36 g; Chemplex). This mixture washeated to 120° F. (49° C.), and kept at this temperature for theduration of the study. The sample of the invention was prepared bybasifying some of the stock solution of aqueous KCl with WELLGUARD™ 7137(355 g) to pH 10.5 with dilute aqueous Na₂CO₃ (0.1 M). This solution wassheared with guar (3.36 g; Chemplex Industries, Inc.) for 3 minutes.This mixture was heated to 120° F. (49° C.), and kept at thistemperature for the duration of the study.

Table 1 summarizes the viscosity time dependence for these well fluids.In the inventive well fluid, the viscosity decay at hour 22 was minimal,but by hour 146 the viscosity decay was significant. Table 2 summarizesthe time dependence of the presence of residual WELLGUARD™ 7137,measured as total Br₂. In this guar well fluid, the residual decay alsoto be relatively rapid. Variables for this guar system were notoptimized.

TABLE 1 Ex. Polymer Breaker 4 hr. 22 hr. 146 hr. 242 hr. 1a* xanthannone 715 cP 803 cP 1900 cP  1780 cP  1b xanthan WELLGUARD ™ 7137 116 cP229 cP  195 cP  215 cP 2a* guar none —  37 cP 13.1 cP 12.7 cP 2b guarWELLGUARD ™ 7137 — 1.23 cP  1.23 cP 1.41 cP 3a* guar, pH 10.5 none — 189cP  121 cP  128 cP 3b guar, pH 10.5 WELLGUARD ™ 7137 — 164 cP 14.5 cP10.2 cP *Comparative examples

TABLE 2 Ex Polymer Breaker 0 hr. 22 hr. 146 hr. 242 hr. 1b xanthanWELLGUARD ™ 7137 981 ppm 651 ppm 446 ppm 395 ppm as Br₂ as Br₂ as Br₂ asBr₂ 2b guar WELLGUARD ™ 7137 981 ppm 33 ppm 1.2 ppm 1.8 ppm as Br₂ asBr₂ as Br₂ as Br₂ 3b guar, WELLGUARD ™ 7137 981 ppm 4 ppm 2 ppm 1.6 ppmpH 10.5 as Br₂ as Br₂ as Br₂ as Br₂

Further embodiments of the invention include:

aa) A process which comprises contacting a sulfamate stabilized,bromine-based breaker with an aqueous polysaccharide fracturing fluidfor use in subterranean oil and gas wells, with said breaker in suchamount to reduce the viscosity of said fracturing fluid, wherein saidactive bromine content of the breaker is at least 100,000 ppm.

ab) A process which comprises contacting a sulfamate stabilized,bromine-based breaker with an aqueous polysaccharide fracturing fluidfor use in subterranean oil and gas wells, with said breaker in suchamount to reduce the viscosity of said fracturing fluid, wherein theamount of said breaker used provides in the range of about 1 to about10,000 ppm of active bromine species in the blended well fluid prior towell application.

ac) A process which comprises contacting a sulfamate stabilized,bromine-based breaker with an aqueous polysaccharide fracturing fluidfor use in subterranean oil and gas wells, with said breaker in suchamount to reduce the viscosity of said fracturing fluid, wherein saidbreaker is formed from

(A) a halogen source which is (i) bromine chloride, (ii) bromine andchlorine, (iii) bromine, or (iv) a mixture of any two or more of (i),(ii), and (iii),

(B) a source of sulfamate anions,

(C) alkali metal base, and

(D) water,

in amounts such that the breaker has an active bromine content of atleast 50,000 ppm, and an atom ratio of nitrogen to active bromineoriginating from (A) and (B) that is greater than about 0.93.

ad) A process as in ac) wherein said halogen source is bromine chloride,bromine and chlorine, or a mixture of bromine chloride and bromine.

ae) A process as in to ac) wherein the content of dissolved activebromine in said breaker is greater than about 160,000 ppm.

af) A process as in ac) wherein the content of dissolved active brominein said breaker is in the range of about 176,000 ppm to about 190,000ppm.

ag) A process according to ac) wherein the content of dissolved activebromine in said breaker is in the range of about 201,000 ppm to about215,000 ppm.

ah) A process as in ac) wherein said halogen source consists essentiallyof bromine chloride, and wherein said alkali metal base is a sodiumbase.

ai) A process as in to ac) wherein said halogen source consistsessentially of bromine chloride, and wherein said active bromine contentof the breaker is at least 100,000 ppm.

aj) A process as in ac) wherein said active bromine content of thebreaker is at least 100,000 ppm, and wherein said atom ratio of nitrogento active bromine originating from (A) and (B) is at least about 1.

ak) A process as in ac) wherein said halogen source consists essentiallyof bromine chloride, and wherein the pH of the breaker is at least about12.

al) A process as in ac) wherein said halogen source consists essentiallyof bromine chloride, and said atom ratio of nitrogen to active bromineoriginating from (A) and (B) is at least about 1.

am) A process as in ac) wherein said halogen source consists essentiallyof bromine chloride, wherein said active bromine content of the breakeris at least 100,000 ppm, and wherein said atom ratio of nitrogen toactive bromine originating from (A) and (B) is at least about 1.

an) A process as in ac) wherein said halogen source consists essentiallyof bromine chloride, wherein said alkali metal base is a sodium base,and wherein said active bromine content of the breaker is at least100,000 ppm.

ao) A process as in ac) wherein said alkali metal base is a sodium base,wherein said active bromine content of the breaker is at least 100,000ppm, and wherein said atom ratio of nitrogen to active bromineoriginating from (A) and (B) is at least about 1.

ap) A process as in ac) wherein said halogen source consists essentiallyof bromine chloride, wherein said alkali metal base is a sodium base,and wherein the pH of the breaker is at least about 12.

aq) A process as in any of ac), ah), or an)-ap) wherein said alkalimetal base is sodium hydroxide.

ar) A process as in ac) wherein said halogen source consists essentiallyof bromine chloride, and wherein said active bromine content of thebreaker is at least 140,000 ppm.

as) A process as in ac) wherein said halogen source consists essentiallyof bromine chloride, and wherein said atom ratio of nitrogen to activebromine originating from (A) and (B) is at least about 1.1.

at) A process as in ac) wherein said halogen source consists essentiallyof bromine chloride, and wherein the pH of the breaker is at least about13.

au) A process as in ac) wherein said halogen source consists essentiallyof bromine chloride, wherein said active bromine content of the breakeris at least 140,000 ppm, and wherein said atom ratio of nitrogen toactive bromine originating from (A) and (B) is at least about 1.1.

av) A process as in ac) wherein said active bromine content of thebreaker is at least 140,000 ppm, and wherein said atom ratio of nitrogento active bromine originating from (A) and (B) is at least about 1.1.

aw) A process as in ac) wherein said active bromine content of thebreaker is at least 140,000 ppm, wherein said atom ratio of nitrogen toactive bromine originating from (A) and (B) is at least about 1.1, andwherein the pH of the breaker is at least about 13.

ax) A process as in ac) wherein said atom ratio of nitrogen to activebromine originating from (A) and (B) is at least about 1.1, and whereinthe pH of the breaker is at least about 13.

ay) A process according to ac) wherein said active bromine content ofthe breaker is at least 140,000 ppm.

az) A process according to ac) wherein said atom ratio of nitrogen toactive bromine originating from (A) and (B) is at least about 1.1.

ba) A process according to ac) wherein the pH of the breaker is at leastabout 13.

bb) A composition for use in decreasing the viscosity of an aqueouspolysaccharide fracturing fluid for use in subterranean oil and gaswells, said composition being comprised of a sulfamate stabilized,bromine-based breaker, wherein said active bromine content of thebreaker is at least 100,000 ppm.

bc) A composition for use in decreasing the viscosity of an aqueouspolysaccharide fracturing fluid for use in subterranean oil and gaswells, said composition being comprised of a sulfamate stabilized,bromine-based breaker, wherein said breaker is formed from

(A) a halogen source which is (i) bromine chloride, (ii) bromine andchlorine, (iii) bromine, or (iv) a mixture of any two or more of (i),(ii), and (iii),

(B) a source of sulfamate anions,

(C) alkali metal base, and

(D) water, in amounts such that the breaker has an active brominecontent of at least 50,000 ppm, and an atom ratio of nitrogen to activebromine originating from (A) and (B) that is greater than about 0.93.

bd) A composition as in bc) wherein said halogen source is brominechloride, bromine and chlorine, or a mixture of bromine chloride andbromine.

be) A composition as in to bc) wherein the content of dissolved activebromine in said breaker is greater than about 160,000 ppm.

-   -   bf) A composition as in bc) wherein the content of dissolved        active bromine in said breaker is in the range of about 176,000        ppm to about 190,000 ppm.

bg) A composition according to bc) wherein the content of dissolvedactive bromine in said breaker is in the range of about 201,000 ppm toabout 215,000 ppm.

bh) A composition as in bc) wherein said halogen source consistsessentially of bromine chloride, and wherein said alkali metal base is asodium base.

bi) A composition as in to bc) wherein said halogen source consistsessentially of bromine chloride, and wherein said active bromine contentof the breaker is at least 100,000 ppm.

bj) A composition as in bc) wherein said active bromine content of thebreaker is at least 100,000 ppm, and wherein said atom ratio of nitrogento active bromine originating from (A) and (B) is at least about 1.

bk) A composition as in bc) wherein said halogen source consistsessentially of bromine chloride, and wherein the pH of the breaker is atleast about 12.

bl) A composition as in bc) wherein said halogen source consistsessentially of bromine chloride, and said atom ratio of nitrogen toactive bromine originating from (A) and (B) is at least about 1.

bm) A composition as in bc) wherein said halogen source consistsessentially of bromine chloride, wherein said active bromine content ofthe breaker is at least 100,000 ppm, and wherein said atom ratio ofnitrogen to active bromine originating from (A) and (B) is at leastabout 1.

bn) A composition as in bc) wherein said halogen source consistsessentially of bromine chloride, wherein said alkali metal base is asodium base, and wherein said active bromine content of the breaker isat least 100,000 ppm.

bo) A composition as in bc) wherein said alkali metal base is a sodiumbase, wherein said active bromine content of the breaker is at least100,000 ppm, and wherein said atom ratio of nitrogen to active bromineoriginating from (A) and (B) is at least about 1.

bp) A composition as in bc) wherein said halogen source consistsessentially of bromine chloride, wherein said alkali metal base is asodium base, and wherein the pH of the breaker is at least about 12.

bq) A composition as in any of bc), bh), or bn)-bp) wherein said alkalimetal base is sodium hydroxide.

br) A composition as in bc) wherein said halogen source consistsessentially of bromine chloride, and wherein said active bromine contentof the breaker is at least 140,000 ppm.

bs) A composition as in bc) wherein said halogen source consistsessentially of bromine chloride, and wherein said atom ratio of nitrogento active bromine originating from (A) and (B) is at least about 1.1.

bt) A composition as in bc) wherein said halogen source consistsessentially of bromine chloride, and wherein the pH of the breaker is atleast about 13.

bu) A composition as in bc) wherein said halogen source consistsessentially of bromine chloride, wherein said active bromine content ofthe breaker is at least 140,000 ppm, and wherein said atom ratio ofnitrogen to active bromine originating from (A) and (B) is at leastabout 1.1.

bv) A composition as in bc) wherein said active bromine content of thebreaker is at least 140,000 ppm, and wherein said atom ratio of nitrogento active bromine originating from (A) and (B) is at least about 1.1.

bw) A composition as in bc) wherein said active bromine content of thebreaker is at least 140,000 ppm, wherein said atom ratio of nitrogen toactive bromine originating from (A) and (B) is at least about 1.1, andwherein the pH of the breaker is at least about 13.

bx) A composition as in bc) wherein said atom ratio of nitrogen toactive bromine originating from (A) and (B) is at least about 1.1, andwherein the pH of the breaker is at least about 13.

by) A composition according to bc) wherein said active bromine contentof the breaker is at least 140,000 ppm.

bz) A composition according to bc) wherein said atom ratio of nitrogento active bromine originating from (A) and (B) is at least about 1.1.

ca) A composition according to bc) wherein the pH of the breaker is atleast about 13.

cb) A process as in ab) wherein said breaker used provides in the rangeof about 100 to about 2000 ppm of active bromine species in the blendedwell fluid prior to well application.

It is to be understood that the reactants and components referred to bychemical name or formula anywhere in this document, whether referred toin the singular or plural, are identified as they exist prior to cominginto contact with another substance referred to by chemical name orchemical type (e.g., another reactant, a solvent, or etc.). It mattersnot what preliminary chemical changes, transformations and/or reactions,if any, take place in the resulting mixture or solution or reactionmedium as such changes, transformations and/or reactions are the naturalresult of bringing the specified reactants and/or components togetherunder the conditions called for pursuant to this disclosure. Thus thereactants and components are identified as ingredients to be broughttogether in connection with performing a desired chemical operation orreaction or in forming a mixture to be used in conducting a desiredoperation or reaction. Also, even though an embodiment and/or the claimsmay refer to substances, components and/or ingredients in the presenttense (“is comprised of”, “comprises”, “is”, etc.), the reference is tothe substance, component or ingredient as it existed at the time justbefore it was first contacted, blended or mixed with one or more othersubstances, components and/or ingredients in accordance with the presentdisclosure.

Except as may be expressly otherwise indicated, the article “a” or “an”if and as used herein is not intended to limit, and should not beconstrued as limiting, the description or a claim to a single element towhich the article refers. Rather, the article “a” or “an” if and as usedherein is intended to cover one or more such elements, unless the textexpressly indicates otherwise.

Each and every patent or other publication or published documentreferred to in any portion of this specification is incorporated in totointo this disclosure by reference, as if fully set forth herein.

This invention is susceptible to considerable variation within thespirit and scope of the appended claims.

1. A composition for use in subterranean oil and gas wells, whichcomposition comprises a sulfamate stabilized, bromine-based breaker, anaqueous polysaccharide fracturing fluid, and a proppant, wherein saidbreaker is present in the composition in an amount that provides in therange of about 100 to about 2000 ppm of active bromine species.
 2. Acomposition as in claim 1 wherein said breaker is formed from (A) ahalogen source which is (i) bromine chloride, (ii) bromine and chlorine,(iii) bromine, or (iv) a mixture of any two or more of (i), (ii), and(iii), (B) a source of sulfamate anions, (C) alkali metal base, and (D)water, in amounts such that the breaker has an atom ratio of nitrogen toactive bromine originating from (A) and (B) that is greater than about0.93.
 3. A composition as in claim 2 wherein said alkali metal base is asodium or potassium base.
 4. A composition as in claim 2 wherein saidhalogen source is bromine chloride, bromine and chlorine, or a mixtureof bromine chloride and bromine, and wherein said alkali metal base is asodium or potassium base.
 5. A composition as in claim 2 wherein saidhalogen source consists essentially of bromine chloride.
 6. Acomposition as in claim 2 wherein said alkali metal base is a sodiumbase.
 7. A composition as in claim 2 wherein said atom ratio of nitrogento active bromine originating from (A) and (B) is at least about
 1. 8. Acomposition as in claim 2 wherein the pH of the breaker is at leastabout
 12. 9. A composition as in claim 2 wherein said halogen sourceconsists essentially of bromine chloride; wherein said alkali metal baseis a sodium base; wherein said atom ratio of nitrogen to active bromineoriginating from (A) and (B) is at least about 1; and wherein the pH ofthe breaker is at least about
 12. 10. A composition as in claim 2wherein said halogen source consists essentially of bromine chloride,wherein the alkali metal base is sodium hydroxide, the atom ratio ofnitrogen to active bromine originating from (A) and (B) is at leastabout 1.1, and the pH of the breaker is at least about
 13. 11. Acomposition as in claim 1 wherein said breaker is formed from brominechloride, bromine and chlorine, or a mixture of bromine chloride and upto about 50 mole % of bromine.
 12. A composition as in claim 1 whereinsaid breaker is a solid-state composition formed by removal of waterfrom an aqueous solution or slurry of a product formed in water from (I)a halogen source which is (i) bromine, (ii) bromine chloride, (iii) amixture of bromine chloride and bromine, (iv) bromine and chlorine in aBr₂ to Cl₂ molar ratio of at least about 1, or (v) bromine chloride,bromine, and chlorine in proportions such that the total Br₂ to Cl₂molar ratio is at least about 1; and (II) a source of overbasedsulfamate which is (i) an alkali metal salt of sulfamic acid and/orsulfamic acid, and (ii) an alkali metal base, wherein said aqueoussolution or slurry has a pH of at least 7, and an atom ratio of nitrogento active bromine from (I) and (II) of greater than 0.93.
 13. A processwhich comprises providing a composition comprising a sulfamatestabilized, bromine-based breaker, an aqueous polysaccharide fracturingfluid, and a proppant intermittently to a well or continuously to awell, wherein said breaker is present in the composition in an amountthat provides in the range of about 100 to about 2000 ppm of activebromine species prior to well application.
 14. A process as in claim 13wherein said breaker is formed from (A) a halogen source which is (i)bromine chloride, (ii) bromine and chlorine, (iii) bromine, or (iv) amixture of any two or more of (i), (ii), and (iii), (B) a source ofsulfamate anions, (C) alkali metal base, and (D) water, in amounts suchthat the breaker has an atom ratio of nitrogen to active bromineoriginating from (A) and (B) that is greater than about 0.93.
 15. Aprocess as in claim 14 wherein said halogen source is bromine chloride,bromine and chlorine, or a mixture of bromine chloride and bromine, andwherein said alkali metal base is a sodium or potassium base.
 16. Aprocess as in claim 14 wherein said halogen source consists essentiallyof bromine chloride.
 17. A process as in claim 14 wherein said alkalimetal base is a sodium base or a potassium base; wherein said atom ratioof nitrogen to active bromine originating from (A) and (B) is at leastabout 1; and wherein the pH of the breaker is at least about
 12. 18. Aprocess as in claim 13 wherein said breaker is formed from brominechloride, bromine and chlorine, or a mixture of bromine chloride and upto about 50 mole % of bromine.
 19. A process as in claim 13 wherein saidbreaker is a solid-state composition formed by removal of water from anaqueous solution or slurry of a product formed in water from (I) ahalogen source which is (i) bromine, (ii) bromine chloride, (iii) amixture of bromine chloride and bromine, (iv) bromine and chlorine in aBr₂ to Cl₂ molar ratio of at least about 1, or (v) bromine chloride,bromine, and chlorine in proportions such that the total Br₂ to Cl₂molar ratio is at least about 1; and (II) a source of overbasedsulfamate which is (i) an alkali metal salt of sulfamic acid and/orsulfamic acid, and (ii) an alkali metal base, wherein said aqueoussolution or slurry has a pH of at least 7, and an atom ratio of nitrogento active bromine from (I) and (II) of greater than 0.93.